A letter from the Independent Parliamentary Standards Authority (Ipsa) revealed the city MP noted on his claims offensive remarks, telling one official they were ‘talking sh*te’, and condemning another as a ‘pedantic SOAB’.

Ipsa Chief Executive Andrew McDonald wrote to Karl McCartney after the Lincoln MP spoke in the House of Commons, and suggested the watchdog used “bullying tactics and threats to try and silence” him.

Karl McCartney said during Business Questions: “What do you think that subsequent to me raising these issues of Ipsa’s senior management’s bullying tactics and threats to try and silence me regarding their spiralling costs?

“Do you think that their chief executive should show some backbone and meet with me as he refused to do so for over two and a half years, instead of attempting to smear Members of Parliament’s names by false innuendo and subterfuge?”

Andrew McDonald rejected the claims and wrote to Karl McCartney: “Some of the notes written by you, and attached to your claims, were recently brought to my attention.

“Having reviewed those notes, I was taken aback by the content, which ranged from the abusive (“you are a pedantic SOAB, aren’t you?”) through to the offensive (“you’re talking shite”) and on to the condescending (“simples – or didn’t you do Geography at Eton and Oxford…”).

“We will do all that is reasonable to shield our team from such treatment. I had hoped it would be possible to address this behaviour without writing to you formally. In the light of your comments today, I write to ask that you conduct your dealings with us – orally or in writing – in civil terms.”

Karl McCartney later told The Lincolnite: “I apologise unreservedly to Ipsa for my comments which were inappropriate, and which I regret having made.

“I accept that such comments have given cause for offence. You will not see me making similar remarks in the future in respect of Ipsa, which has a difficult and important job to do,” the Lincoln MP added.

Lucy Rigby, Labour MP candidate for Lincoln, commented: “It is absolutely and genuinely shocking that Lincoln’s MP would use this kind of language in letters to any body or organisation.”